Boil all broth in heavy large skillet over medium-high heat until reduced to 1 cup, about 12 minutes. Add cream, mushrooms, and onions. Boil until sauce coats vegetables, tossing occasionally, about 6 minutes. Season sauce to taste with salt and pepper. Set aside.

Drain marinade from beef into medium saucepan; boil 2 minutes. Cook beef over hottest part of grill until brown, about 5 minutes per side. Move beef to coolest part of grill; cover and cook until thermometer inserted into center registers 135°F for medium-rare, turning occasionally and basting with marinade, about 30 minutes. Transfer to cutting board; let rest 10 minutes.